JPH1154246A - Ceramic heating body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the deterioration of electrical characteristics and improve high temperature durability by specifying a maximum difference of the resistance value at ordinary temperature of each heating part, including a lead part. SOLUTION: A ceramic heating body 1 is provided with a plurality of heating parts 2 composed of inorganic conductive material formed in layer shape with U-shape cross section and arranged at one end of an insulting member 5, a layered lead pattern part at least a part of it is overlapped in each end part of the heating part 2, a lead wire 7 connected to the other end of the lead pattern part 6, and an electrode unloading part 4 overlapped with the other end side of the lead wire 7 and exposed to the other end outer peripheral surface of the insulating member 5. Two sets of these parts in the electrically connected state are disposed in parallel in the insulating member 5. The largest difference between the respective resistance values including the lead parts of a plurality of heating parts 2 is within 30% of the maximum value of the resistance value, so that electrical load applied to each heating part 2 is uniformized to make the surface temperature uniform, and heating efficiency is improved without accelerating the change of insulating characteristic and heating characteristic due to difference of electrical or thermal change with the lapse of time nature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel vaporization and ignition heater for glow plugs and oil fan heaters for internal combustion engines, which has excellent thermal shock resistance, high-temperature stability, good temperature rising characteristics and durability, and heaters for various sensors. For ceramic heaters that are applied to general heaters for household use, electronic components, industrial equipment, etc., such as heaters for hot water, soldering irons, etc., and are most suitable for high temperatures used with DC or AC power supplies It is.

[0002]

2. Description of the Related Art Conventionally, various ignition and heating heaters such as a glow plug for an internal combustion engine used for rapidly preheating the sub-combustion chamber at the time of starting or idling a diesel engine are made of heat-resistant metals. Various types of sheathed heaters in which a heat-generating resistor made of a high-melting metal wire or the like is embedded in a sheath together with heat-resistant insulating powder, and various ignition devices utilizing spark discharge have been frequently used.

However, all of them are difficult to raise the temperature rapidly, and furthermore, they are inferior in durability such as abrasion resistance, heat resistance, corrosion resistance and the like. In particular, in an ignition device using the above-mentioned spark discharge, noise is generated at the time of ignition. In addition to the above, there are drawbacks such as easy occurrence of radio interference and lack of reliability in terms of reliable ignition.

[0004] Therefore, the heat conduction efficiency is excellent, rapid temperature rise is possible, no radio wave interference occurs, and reliable ignition and high safety, and excellent durability such as wear resistance, heat resistance, corrosion resistance, etc. As a highly heat-generating element, a heat-generating part consisting of a high-melting-point metal or its compound, and a heat-generating resistor of various inorganic conductive materials containing them as a main component is carried on an electrically insulating ceramic sintered body having good heat conductivity. A ceramic heating element integrated by bonding or burying has been widely used as various ignition and heating heaters, including glow plugs for internal combustion engines.

As an insulating member of such a ceramic heating element, an oxide ceramic mainly composed of alumina (Al ₂ O ₃ ) is frequently used, and as an inorganic conductive material, tungsten (W), molybdenum (Mo), or the like is used. It is known that a heating resistor made of a high-melting-point metal is used as the heating part. However, such a ceramic heating element is limited to applications at a relatively low temperature of up to about 900 ° C even for soldering irons and sensor heating. It had been.

Therefore, as a ceramic heating element for high temperatures exceeding 900 ° C., a non-oxide ceramic represented by silicon nitride (Si ₃ N ₄ ) is used as an insulating member, and as an inorganic conductive material, in addition to the high melting point metal, Tungsten carbide (WC)
Or molybdenum silicide (MoSi ₂ ), titanium nitride (Ti
There has been proposed a compound formed by combining a compound of a high melting point metal such as N) or a heat generating portion composed of a heat generating resistor containing the compound as a main component.

[0007] Among them, as a ceramic heater having excellent durability against thermal shocks and physical shocks, an insulator made of electrically insulating ceramics containing silicon nitride as a main component and an electric resistance made of electrically conductive ceramics in an insulator made of silicon nitride. A body in which two layers are buried in parallel at a predetermined interval has been proposed (see Japanese Patent No. 2537273).

[0008]

However, if there is a difference between the resistance values of the two-layered electrical resistors in the ceramic heater, the two-layered electrical resistors are electrically connected in parallel at the electrode extraction portion of the ceramic heater. Therefore, the current flows preferentially to the electric resistor having the lower resistance value due to energization, and heat is generated first to cause a temperature difference, so that the surface temperature distribution of the ceramic heater may not be uniform.

Further, when heating and cooling are repeated in the above-described state, electrical or thermal changes over time such as an increase in resistance and disconnection of the two-layer electric resistor are different from each other.
There has been a problem that long-term reliability is poor due to changes in insulation characteristics and heat generation characteristics.

[0010] Further, a ceramic heater, which is formed in two layers at a predetermined interval and has a buried cross section when the electric resistor has a U-shape when viewed in plan, is embedded in a glow plug for an internal combustion engine, and for various ignitions. When applied to a high temperature exceeding 900 ° C. as a heater for heating, generally 1000 to 1000
1300 ° C and then exposed to the ignited flame
The temperature exceeds 350 ° C. and reaches 1400 ° C., and the ceramic heater cracks due to dielectric breakdown from repeated heating and cooling at such a high temperature.
In general, the glow plug requires 850 hours or more as a durable time until the resistance change exceeds 10% of an initial value. On the other hand, there is a possibility that a resistance change exceeding 10% occurs in a short time. There is a problem that the durability is poor in practical use.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to use a DC or AC power supply to instantaneously generate heat from a temperature near normal temperature to a temperature as high as 1000 ° C. over a long period of time. Or the continuous operation at a high temperature of 1000 ° C. or more for a long time, the deterioration of the heat generating portion composed of the heat generating resistor made of the inorganic conductive material is small, and the insulating member may be cracked due to the deterioration of the insulating property or the like. It is another object of the present invention to provide a ceramic heating element having excellent high-temperature durability.

[0012]

As a result of various studies on the above-mentioned problems, the present inventor has found that each heat-generating portion is composed of a plurality of heat-generating resistors of inorganic conductive material which are provided in parallel at a predetermined interval and constitute a ceramic heat-generating body. It has been found that the variation in the resistance value of the ceramic heating element affects the electrical characteristic deterioration and the high-temperature durability of the ceramic heating element due to energized heat generation. The present inventors have found that deterioration in characteristics can be reduced and high-temperature durability can be improved, leading to the present invention.

That is, the ceramic heating element of the present invention comprises a plurality of heating portions made of an inorganic conductive material which is provided in parallel at a predetermined interval and which generates heat when energized, a lead portion electrically connected to the heating portion, The ceramic sintered body having the lead portion and an electrode connection portion electrically connected to each other is used as an insulating member, and the maximum difference between the resistance values of the heat generating portions including the lead portion at room temperature is the resistance value. 30% of the maximum resistance value
It is characterized by being within.

In particular, the maximum difference between the resistance values is preferably within 22% of the maximum resistance value among the respective resistance values, and the insulating member made of the ceramic sintered body is preferably a non-oxide ceramic. Of these, those made of a silicon nitride-based sintered body are more desirable.

[0015]

According to the ceramic heating element of the present invention, the maximum difference between the resistance values including the lead portions of a plurality of heating portions provided in parallel at a predetermined interval is within 30% of the maximum value of the resistance value. Therefore, the electric load applied to each of the heat generating portions is uniformed, the surface temperature is also uniformed, and changes in insulation characteristics and heat generation characteristics due to differences in electrical or thermal changes over time are not accelerated. Heat generation efficiency is good, and high-temperature durability and reliability are improved.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a ceramic heating element according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view showing an embodiment of the ceramic heating element of the present invention, and FIGS. 2 and 3 are perspective views showing other examples of the ceramic heating element of the present invention.

In FIG. 1, reference numeral 1 denotes a heat generating portion 2 made of an inorganic conductive material which generates heat when energized, a lead portion 3 made of a lead pattern portion 6 and a lead wire 7 made of a lower resistance inorganic conductive material, and an electrode take-out portion. 4 is a ceramic heating element embedded in an insulating member 5 made of a ceramic sintered body.

The ceramic heating element 1 has a heating portion 2 made of an inorganic conductive material formed in a layer and having a U-shaped cross section when viewed in a plan view at one end of an insulating member 5, and each end of the heating portion 2. Layered lead pattern portion 6 at least partially overlapped with the portion
And a lead wire 7 at the other end of the lead pattern portion 6, respectively.
Are connected to each other, and two sets of the electrode lead portions 4 are provided so as to be superposed on the other end side of the lead wire 7 and exposed on the outer peripheral surface of the other end of the insulating member 5 and electrically connected to each other. 5, the tip of the insulating member on the side of the heat generating portion 2 has a substantially spherical shape, and at least a portion corresponding to the highest heat generating portion has a circular cross section.

According to the present invention, the plurality of heat generating portions 2 arranged in parallel to each other and constituting the heat generating portion have a maximum difference between the resistance values of each heat generating portion including the lead portion, which is 30 times the maximum value of each resistance value. %, The heat generating portion formed of a heat generating resistor made of an inorganic conductive material is greatly deteriorated, and the insulating member is cracked due to a decrease in insulation, and the high-temperature durability is significantly deteriorated.

Therefore, the variation of the resistance value of the heat generating portion including the lead portion is limited to the above 30%, but the electric load applied to each heat generating portion can be made uniform, and efficient heat generation becomes possible. From the viewpoint of little deterioration in electrical characteristics and improvement in high-temperature durability and reliability, the resistance value of each heating portion including the lead portion was measured, and the maximum difference was the maximum value among the measured resistance values. Is more preferably within 22%.

The heat generating portion 2 constituting the ceramic heat generating element 1 of the present invention is formed of a block of inorganic conductive material facing in parallel and having a U-shaped cross section when viewed in plan as shown in FIG. Alternatively, the lead portion 3 may be directly connected to the block by a lead wire, and the end portion of the lead wire may be exposed to the outer periphery of the insulating member 5 to form the electrode extraction portion 4.

On the other hand, in FIGS. 1 and 2, the outer shape of the insulating member 5 is a cylindrical shape with a rounded tip. However, the outer shape of the insulating member 5 is not limited to this, and as shown in FIG. The outer shape of the insulating member 5 may be a substantially rectangular parallelepiped shape, and the heat generating portion 2, the lead portion 3, and the electrode take-out portion 4 to be embedded may be integrally formed by printing or the like.

As described above, when the heat-generating part 2, the lead part 3, and the electrode take-out part 4 are integrally formed by printing, for example, the heat-generating part 2, the lead part 3, and the electrode take-out part 4 each have almost the same thickness. Keep the lead width constant by changing the line width
In addition, the resistance value of the electrode take-out unit 4 may be set lower than that of the heat-generating unit 2.

In the present invention, the heat generating portion may be made of any material as long as it is an inorganic conductive material which can be fired simultaneously with the insulating member. For example, high melting point metals such as W, Mo, Re, Cr and Ta, W, Mo, and the like can be used. Ta, Ti, Z besides Re and Cr
Compounds of nitrides, carbides, silicides, borides of Group 4a and Group 5a elements such as r, Hf, V, and Nb, and heat-generating resistors containing these compounds as main components, especially for high-temperature applications In the case where Si ₃ N ₄ is used as the main component of the insulating member, it is difficult to react even at a high temperature due to a difference in thermal expansion from the material, and WC is optimal in terms of ease of handling and high-temperature durability. is there.

When the above-mentioned inorganic conductive material is used as a main component, silicon nitride, boron nitride, carbide, etc. may be used as a dispersing material in order to prevent cracks due to the difference in thermal expansion from the insulating member and not to increase the resistance. Silicon or one or more of alumina and the like may be added as appropriate,
For example, with respect to 100 parts by weight of the main component, 5
It is preferable that the amount is 30 to 30 parts by weight, 1 to 15 parts by weight for boron nitride, 3 to 15 parts by weight for silicon carbide, and 30 parts by weight or less for alumina.

On the other hand, the heat generating portion in the present invention may be any of a layer, a block, and a line as described above, and is constituted by two or more in parallel, and has a U-shaped or W-shaped cross section when viewed in plan. Although it can be applied in various shapes such as a letter shape, a zigzag shape, etc., in order to prevent dielectric breakdown under the use condition as described above, the plurality of heating resistors should be provided at a distance of 0.2 mm or more from each other. is necessary.

In particular, when a layered heat generating portion is formed by a printing method, the thickness of the heat generating portion is set to a resistance value for a DC power supply up to about 50 V from the viewpoint of preventing occurrence of cracks or the like in the heat generating portion. Then, at least in the highest heat generating part, 5-150
A thickness in the range of μm is desirable, especially a thickness in the range of 10 to 50 μm.

The lead portion is made of an inorganic conductive material which can be fired at the same time as the insulating member, similarly to the heat generating portion, and may be made of any material having a lower resistance than the heat generating portion. For example, W, Mo, Re, In addition to refractory metals such as Cr and Ta, W, Mo, Re, and Cr, Ta, Ti, Zr, and H
Compounds of nitrides, carbides, silicides, borides of elements of groups 4a and 5a such as f, V, Nb, and the like, or a conductive material having a low thermal expansion coefficient containing these compounds as a main component are desirable. Alternatively, a rod-shaped material formed by an extrusion molding method or an injection molding method, or a layered material formed by a screen printing method may be used.

Further, the electrode take-out portion can be made of the same material as that of the lead portion, and may be formed such that the lead portion is directly exposed or electrically connected to the lead member by a screen printing method. .

The insulating member is desirably a non-oxide ceramic sintered body such as silicon nitride, sialon, or aluminum nitride for high-temperature use. In particular, a silicon nitride-based sintered body is sintered to Si ₃ N ₄ powder. As a binding aid, there is one using an oxide of an element of Group 3a of the periodic table such as yttrium (Y). From the viewpoint of suppressing ion transfer at a high temperature, Yb ₂ O is used as a sintering aid. ₃ is desirable, that the grain boundary phase so as to precipitate a crystal phase or glass phase including a periodic table group 3a elements, silicon and the like of the sintering auxiliary component are preferred.

Further, in order to adjust the thermal expansion with the heat generating portion, the silicon nitride sintered body has a larger thermal expansion coefficient M
It is also effective to add one or more silicides, carbides, nitrides, and borides such as o and W.

[0032]

Next, the ceramic heating element of the present invention was evaluated as described in detail below. First, the specific surface area is 7 to 15
At m ² / g, the oxygen content is 1.
Si ₃ N ₄ powder containing 5% by weight or less and metal impurities in a total amount of 0.05% by weight or less was mixed with RE ₂ O ₃ of an oxide of a Group 3a element (RE) of the periodic table as a sintering aid. , Al ₂ O
_3. MoSi ₂ powders were weighed so as to be 10% by weight, 2% by weight, and 4% by weight, respectively, and a granulated body was prepared from a slurry prepared by mixing them, and the granulated body was press-formed. A plate-like molded body was obtained by a known molding method such as a method.

On the other hand, 80% by weight of WC fine powder and Si ₃ N
₄ A paste prepared by adding a solvent such as butyl acetate to a mixed powder of 20% by weight of the fine powder is used for forming a heat generating portion, and the paste is mixed with a mixed powder of 85% by weight of the WC fine powder and 15% by weight of the Si ₃ N ₄ fine powder. A paste prepared by adding the same solvent was used for forming a lead pattern portion and an electrode extraction portion.

Next, a U-shaped pattern was formed by screen printing using the obtained paste for forming a heat generating portion, and two U-shaped patterns were respectively placed at positions where the pattern was within 5 mm from the end of the insulating member after sintering. A heating section having a thickness of 80 μm is formed on the surface of the flat molded body.

On the other hand, a lead pattern having a predetermined shape and a thickness of about 50 μm is formed by the same screen printing method using the lead pattern part forming paste so as to partially overlap both ends of the U-shaped pattern. Form a part.

On the other hand, using a paste for forming an electrode lead-out portion having the same composition as the paste for forming a lead pattern portion, a screen having a width of 0.7 mm and a thickness of 0.7 mm was formed on the surface on the other end side by the same screen printing method as described above. Four patterns were formed at predetermined positions in parallel at about 70 μm to the side surface of the molded body, and electrode extraction portions were formed.

Then, a W wire having a diameter of 0.25 mm is placed so as to be connected to a lead pattern portion formed by partially overlapping the heat generating portion and an electrode take-out portion. After laminating the above-mentioned ceramic molded body having the same composition without forming a heating resistor, an electrode take-out part, and the like, the ceramic molded body is heated at 1700 to 1900 ° C. in a reducing atmosphere.
It was fired and integrated for a time.

The periphery of the ceramic heating element material thus obtained is polished to make the tip of the heating section side a spherical surface and a circular cross section, and to expose the end face of each electrode extraction section to the side face of the silicon nitride sintered body. A ceramic heating element having a diameter of 3.5 mm was produced.

Next, a nickel (Ni) film is formed on at least the exposed portion of the electrode portion of the ceramic heating element by a metallizing method, a plating method, or the like. A ceramic heating element for evaluation in which two heat generating portions were buried in parallel at a predetermined interval by bonding with a braze was produced.

First, metallization of the electrode extraction portion of the ceramic heating element for evaluation is performed for each heating element, or the end of the ceramic heating element is ground to expose a lead portion to form a terminal for resistance measurement. At room temperature, measure the resistance of each heating part including the lead using a resistance measurement multimeter,
The ratio to the maximum resistance value was calculated from the difference.

Next, the electrode take-out portion or the lead portion exposed by grinding is connected in parallel by metallizing or the like.
In the same manner as above, the total resistance of the two heat-generating portions provided in parallel including the lead portion was measured.

Thereafter, a DC voltage of 10 to 35 V, which saturates at a heating temperature of 1400 ° C., is applied to the ceramic heating element for evaluation in which the electrode lead-out portions or the exposed lead portions are connected in parallel, thereby applying a voltage around the highest heating portion. The temperature distribution in the direction was measured, the maximum temperature difference was determined, and the temperature distribution was evaluated as the maximum heat generating portion temperature distribution.

A high-load endurance test in which the DC voltage is continuously applied is performed, and the resistance between the two electrodes is measured at regular intervals.
%, It was judged to be defective, and the durability was evaluated by the time when it exceeded 10%.

In this evaluation experiment, no crack was found in the insulating member when the rate of change in resistance was within 10%.

[0045]

[Table 1]

As is clear from the table, Sample No. 5 in which the difference in the resistance value of each heating portion exceeded 30% of the maximum resistance value.
In 9, 21, 29, 31, and 38, the temperature distribution in the circumferential direction of the highest heat generating portion has a temperature difference of 36 ° C. or more, and the durability time is also 7 hours.
While the resistance change exceeds 10% within 96 hours,
In the present invention, the temperature difference in the temperature distribution in the circumferential direction is as low as 34 ° C. or less, and the durability time is 898 hours or more.

In the above-described embodiment, the self-saturated ceramic heating element in which the printed heating element is embedded in the insulating member has been described. However, the present invention is not limited to the above-described embodiment. Anything may be used as long as it does not deviate from the gist of the present invention, and the same effect can be obtained even when applied to a ceramic heating element having a heating part exposed, as well as a self-control type ceramic heating element having a built-in braking coil. is there.

[0048]

As described above, the ceramic heating element of the present invention uses a ceramic sintered body having a plurality of heating parts provided in parallel at a predetermined interval as an insulating member. Since the maximum difference between the resistance values of the respective heating parts at room temperature is controlled to be within 30% of the maximum value of the resistance value, rapid heating to a high temperature is repeated,
Even when the power is applied for a long time, the resistance change of the heat generating part is extremely small. As a result, the heat generating resistor does not break, the insulating member does not crack, and the durability and reliability are excellent. In addition, ceramic heating elements suitable for various types of ignition and heating can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of a ceramic heating element of the present invention.

FIG. 2 is a perspective view showing another example of the ceramic heating element of the present invention.

FIG. 3 is a perspective view showing another example of the ceramic heating element of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic heating element 2 Heating part 3 Lead part 4 Electrode extraction part 5 Insulating member

Claims (3)

[Claims] A plurality of heat generating portions made of an inorganic conductive material that generates heat by energization and provided in parallel at predetermined intervals, a lead portion connected to the heat generating portion, and an electrode extraction portion connected to the lead portion. A ceramic heating element having a ceramic sintered body provided as an insulating member, wherein a maximum difference between resistance values of each heating section including the lead portion at normal temperature is within 30% of the maximum value of the resistance value. Characteristic ceramic heating element. 2. The ceramic heating element according to claim 1, wherein the maximum difference between the resistance values is within 22% of the maximum value of the resistance value. 3. An insulating member made of a ceramic sintered body is a silicon nitride based sintered body.
Alternatively, the ceramic heating element according to claim 2.